.\"
.\" Copyright (c) 2025-2026 Pouria Mousavizadeh Tehrani <pouria@FreeBSD.org>
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.Dd March 31, 2026
.Dt GENEVE 4
.Os
.Sh NAME
.Nm geneve
.Nd Generic Network Virtualization Encapsulation interface
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Cd device geneve
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Cd if_geneve_load="YES"
.Sh DESCRIPTION
The
.Nm
driver creates a generic network virtualization tunnel interfaces
for Tentant Systems over an L3 (IP/UDP) underlay network that provides
a Layer 2 (ethernet) or Layer 3 service using
.Nm
protocol.
.Pp
This driver corresponds to RFC 8926 for format specification and by default
uses the multicast-learning-based approach for its control plane.
To provide control plane independence all of the driver-specific operations
are implemented using
.Xr rtnetlink 4
and all the
.Xr ioctl 2
calls are implemented using the
.Xr nv 9
library.
Each
.Nm
interface is created at runtime using interface cloning.
This is most easily done with the
.Xr ifconfig 8
.Cm create
command or using the
.Va cloned_interfaces
variable in
.Xr rc.conf 5 .
The interface may be removed with the
.Xr ifconfig 8
.Cm destroy
command.
.Pp
The
.Nm
interface must be configured in either L2 or L3 mode.
An L2
.Nm
tunnel could be used as a backplane between the virtual switches
residing in hypervisors, switches, or other appliances.
.Pp
The L3
.Nm
tunnel provides virtualized IP forwarding service similar to IP/VRF.
.Pp
By default the
.Nm
driver creates an L2 interface that supports the usual network
.Xr ioctl 2 Ns s
and thus can be used with
.Xr ifconfig 8
like any other Ethernet interface.
An L2
.Nm
interface encapsulates the Ethernet frame by prepending IP/UDP and
.Nm
headers.
Thus, the encapsulated (inner) frame is able to be transmitted
over a routed, Layer 3 network to the remote host.
.Pp
The
.Nm
interface may be configured in either unicast or multicast mode.
When in unicast mode,
the interface creates a tunnel to a single remote host,
and all traffic is transmitted to that host.
When in multicast mode,
the interface joins an IP multicast group,
and receives packets sent to the group address,
and transmits packets to either the multicast group address,
or directly to the remote host if there is an appropriate
forwarding table entry.
.Pp
When the
.Nm
interface is brought up, a
.Xr udp 4
.Xr socket 9
is created based on the configuration,
such as the local address for unicast mode or
the group address for multicast mode,
and the listening (local) port number.
Since multiple
.Nm
interfaces may be created that either
use the same local address
or join the same group address,
and use the same port,
the driver may share a socket among multiple interfaces.
However, each interface within a socket must belong to
a unique
.Nm
segment per
.Xr vnet 9 .
The analogous
.Xr vlan 4
configuration would be a physical interface configured as
the parent device for multiple VLAN interfaces, each with
a unique VLAN tag.
Each
.Nm
segment is identified by a 24-bit value in the
.Nm
header called the
.Dq Virtual Network Identifier ,
or VNI.
This value can be set with
.Xr ifconfig 8
.Cm geneveid
parameter.
.Pp
When configured with the
.Xr ifconfig 8
.Cm genevelearn
parameter, the interface dynamically creates forwarding table entries
from received packets.
An entry in the forwarding table maps the inner source MAC address
to the outer remote IP address.
During transmit, the interface attempts to lookup an entry for
the encapsulated destination MAC address.
If an entry is found, the IP address in the entry is used to directly
transmit the encapsulated frame to the destination.
Otherwise, when configured in multicast mode,
the interface must flood the frame to all hosts in the group.
The maximum number of entries in the table is configurable with the
.Xr ifconfig 8
.Cm genevemaxaddr
command.
Stale entries in the table are periodically pruned.
The timeout is configurable with the
.Xr ifconfig 8
.Cm genevetimeout
command.
.Ss MTU
Since the
.Nm
interface encapsulates the Ethernet frame with an IP, UDP, and
.Nm
header, the resulting frame may be larger than the MTU of the
physical network.
The
.Nm
specification recommends the physical network MTU be configured
to use jumbo frames to accommodate the encapsulated frame size.
.Pp
By default, the
.Nm
driver sets its MTU to usual ethernet MTU of 1500 bytes, reduced by
the size of geneve headers prepended which is depends on
.Cm genevemode .
.Pp
Alternatively, the
.Xr ifconfig 8
.Cm mtu
command may be used to set the fixed MTU size on the
.Nm
interface to allow the encapsulated frame to fit in the
current MTU of the physical network.
If the
.Cm mtu
command was used, system no longer adjust the
.Nm
interface MTU on routing or address changes.
.Ss Hop Limit
TTL value of
.Nm
interface can change by using the
.Xr ifconfig 8
.Cm genevettl
command and it also can be inherited from carrying packet.
You can set the
.Cm genevettl
to a number value or
.Cm inherit
option to be inherited at the encapsulation and decapsulation point.
.Ss Traffic Class
Just like the TTL value, ToS value can be inherited at the encapsulation point
using
.Xr ifconfig 8
.Cm genevedscpinherit .
As defined in RFC 8926, ECN value follows the RFC 6040 for both ingress and
egress traffic.
.Ss Don't Fragment
To make sure fragmentation does not happing during transmission, you can
set the
.Xr ifconfig 8
.Cm genevedf
value to
.Cm set
value which sets the DF bit on IPv4 header and IP_DONTFRAG option on both IPv4
and IPv6 sockets.
Similar to other options, it can be set to
.Cm inherit
value.
.Ss Multicast
To create the
.Nm
interface with multicast underlay, one must use
.Xr ifconfig 8
.Cm genevegroup
instead of
.Cm geneveremote
and set it to a multicast address (e.g. ff08::db8:0:1, 239.0.0.1).
One can set the outbound multicast interface with
.Xr ifconfig 8
.Cm genevedev
to bound its multicast group to specific interface.
.Pp
The
.Cm ip_mroute
kernel module for IPv4 underlay and
.Cm ip6_mroute
for IPv6 underlay must be loaded for
.Xr multicast 4
to function.
.Sh HARDWARE
The
.Nm
driver supports hardware checksum offload (receive and transmit) and TSO on the
encapsulated traffic over physical interfaces that support these features.
The
.Nm
interface examines the
.Cm genevedev
interface, if one is specified, or the interface hosting the
.Cm genevelocal
address, and configures its capabilities based on the hardware offload
capabilities of that physical interface.
If multiple physical interfaces will transmit or receive traffic for the
.Nm
then they all must have the same hardware capabilities.
The transmit routine of a
.Nm
interface may fail with
.Er ENXIO
if an outbound physical interface does not support
an offload that the
.Nm
interface is requesting.
This can happen if there are multiple physical interfaces involved, with
different hardware capabilities, or an interface capability was disabled after
the
.Nm
interface had already started.
.Sh EXAMPLES
.Bd -literal
       Host A (198.51.100.10)
       +--------------------+
       | VNI 100 10.1.1.0/24|
       | VNI 200 10.2.2.0/24|
       +---------+----------+
                 |
         (198.51.100.0/24)
                 |
 +---------------v---------------+
 | Host B (203.0.113.1)          |
 |        +------+-------+       |
 | geneve0|              |geneve1|
 | +------v----+   +-----v-----+ |
 | | bridge0   |   | bridge1   | |
 | | (VNI 100) |   | (VNI 200) | |
 | +------+----+   +----+------+ |
 |        |             |        |
 +--------v-------------v--------+
   epair0b|             |epair1b
   +------+----+   +----+------+
   | Jail A    |   | Jail B    |
   | (10.1.1.x)|   | (10.2.2.x)|
   +-----------+   +-----------+
.Ed
Assume host A has the (external) IP address 198.51.100.10 and
two internal addresses of 10.1.1.1/24 and 10.2.2.1/24, while
host B has the external address of 203.0.113.10 and two jails
with their own separate
.Xr VNET 9 .
the following commands will configure the tunnel:
.Pp
On host A, create a l2
.Nm
interface in unicast mode:
.Bd -literal
ifconfig geneve0 create geneveid 100 genevelocal 198.51.100.10 geneveremote 203.0.113.1
ifconfig geneve1 create geneveid 200 genevelocal 198.51.100.10 geneveremote 203.0.113.1
.Ed
.Pp
On host B:
.Bd -literal
ifconfig geneve0 create geneveid 100 genevelocal 203.0.113.1 geneveremote 198.51.100.10
ifconfig geneve1 create geneveid 200 genevelocal 203.0.113.1 geneveremote 198.51.100.10
ifconfig bridge0 addm geneve0 addm epair0a
ifconfig bridge1 addm geneve1 addm epair1a
.Ed
.Pp
The example below demonstrate multicast configuration with IPv6:
.Bd -literal
                      ----------- VNI 42 -----------
                     /                              \\
2001:db8::1/64 --- Host A ------ Multicast ------- Host B --- 2001:db8::2/64
                  3fff::1 [em0] ff08::db8:1 [em0]  3fff::2
.Ed
.Pp
Create a
.Nm
interface in multicast mode,
with the
.Cm genevelocal
address of 3fff::1,
and the
.Cm genevegroup
address of ff08::db8:0:1.
The em0 interface will be used to transmit multicast packets.
On host A:
.Bd -literal
ifconfig geneve0 create geneveid 42 genevelocal 3fff::1 genevegroup ff08::db8:1 genevedev em0
.Ed
.Pp
On host B:
.Bd -literal
ifconfig geneve0 create geneveid 42 genevelocal 3fff::2 genevegroup ff08::db8:1 genevedev em0
.Ed
.Pp
Once created, the
.Nm
interface can be configured with
.Xr ifconfig 8 .
.Pp
The following when placed in the file
.Pa /etc/rc.conf
will cause a geneve interface called
.Dq Li geneve0
to be created, and will configure the interface in unicast mode.
.Bd -literal
cloned_interfaces="geneve0"
create_args_geneve0="geneveid 108 genevelocal 192.168.100.1 geneveremote 192.168.100.2"
.Ed
.Sh SEE ALSO
.Xr inet 4 ,
.Xr inet6 4 ,
.Xr multicast 4 ,
.Xr rtnetlink 4 ,
.Xr vlan 4 ,
.Xr rc.conf 5 ,
.Xr ifconfig 8 ,
.Xr sysctl 8
.Rs
.%A "J. Gross, Ed."
.%A "I. Gross, Ed."
.%A "T. Sridhar, Ed."
.%T "Geneve: Generic Network Virtualization Encapsulation"
.%D November 2020
.%O "RFC 8926"
.Re
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written by
.An Seyed Pouria Mousavizadeh Tehrani Aq info@spmzt.net
.Sh BUGS
Current geneve implementation with netlink can't set geneve options
other than genevemode during interface cloning in ifconfig without
specifying the interface index.